瞬态吸收光谱茜素超快动力学研究

激发态质子转移是光物理学、光化学和光生物过程中最基本的化学反应之一。激发态分子内质子转移(excited-state intramolecular proton transfer, ESIPT)通常是指有机分子受到激发，到达激发态后，质子在激发态势能面上从质子供体基团转移到质子受体基团并形成含有分子内氢键多元环的过程, 一般发生在亚皮秒量级。质子转移可应用于有机发光二极管、荧光探针等领域。茜素，即1,2-二羟基蒽醌，可从茜草根部提取，具有与醌类衍生物相似的结构，常用于染料、染色剂和药物等。近年来，发现茜素分子具有质子转移特性，可用来制备新型“绿色”染料敏化电池。利用稳态吸收、稳态荧光和飞秒瞬态吸收光谱技术以及第一性原理理论计算对溶于乙醇溶液的茜素分子的质子转移过程进行了研究和分析。稳态吸收和稳态荧光研究结果表明: 在基态时，茜素分子的正常构型9,10-酮处于稳定状态，容易发生跃迁；在激发态时，茜素分子的互变异构体构型1,10-酮处于稳定状态，容易产生荧光发射。飞秒瞬态吸收光谱测量使用的激光的激发波长为370 nm。测得的瞬态吸收光谱在430 nm附近存在茜素的基态漂白信号。通过使用全局拟合方法对瞬态吸收光谱进行分析研究发现：茜素正常构型9,10-酮的激发态分子内质子转移时间为110.5 fs，茜素互变异构体构型1,10-酮分子内振动弛豫时间为30.7 ps，茜素互变异构体构型1,10-酮荧光寿命为131.7 ps。通过使用单波长动力学拟合的方法对瞬态吸收光谱进行分析发现：发生质子转移的时间尺度与运用全局拟合方法得出的结果基本一致；茜素分子的正常构型9,10-酮分子在110.5 fs的时间尺度内处于快速减少的趋势，而茜素分子的互变异构体构型1,10-酮分子在这一时间尺度内处于快速上升的趋势。当延迟时间增大时，茜素分子的互变异构体构型1,10-酮分子又呈现缓慢衰减的趋势。

Ultrafast Dynamics Investigation on Alizarin by Transient Absorption Spectroscopy

Excited proton transfer is one of the most basic chemical reactions in photo-physics, photochemistry and photobiology. Excited state intramolecular proton transfer (ESIPT) is usually defined as the process of proton transfer from the proton-donor group to the proton-acceptor group on the excited state energy surface, forming intramolecular bond-rings containing hydrogens. When the organic molecules is excited to the excited state, the proton transfer process takes place in a very short time, usually on the sub-picosecond scale. The effect of the proton transfer can be used in organic light-emitting diodes and fluorescent probes. Alizarin, namely 1,2-dihydroxyanthraquinone, extracted from the roots of madder originally, has a similar structure to quinone derivatives and is often used as dyes, dyestuffs and pharmaceuticals. In recent years, alizarin molecules have been found to have proton transfer properties, which can be used to prepare new green dye-sensitized batteries. In this paper, the proton transfer process of alizarin molecules dissolved in ethanol solution is investigated and analyzed by using the steady-state absorption, steady-state fluorescence, femtosecond transient absorption spectroscopy and first-principles calculation. The results of steady-state absorption and steady-state fluorescence show that the normal configuration of alizarin molecule 9,10-ketone is in a stable state in the ground state, which is prone for the energy transition. However, in the excited state, the tautomer 1,10-ketone of alizarin molecule is in a stable state, easy to produce fluorescence emission. Femtosecond transient absorption spectroscopy employs a laser with the excitation wavelength of 370 nm. The measured transient absorption spectra show that the ground state bleaching signal of the alizarin locates at 430 nm wavelength. The global fitting method is used to analyze the transient absorption spectra, and the results show that the proton-transfer time in the excited state of the normal configuration of the alizarin 9,10-ketone is 110.5 femtoseconds, the vibration-relaxation time in alizarin 1,10-ketone tautomer is 30.7 picoseconds, and the fluorescence life of alizarin 1,10-ketone tautomer is 131.7 picoseconds. By using the method of single-wavelength dynamic fitting, the transient absorption spectra are analyzed, and the results for the time scale of proton-transfer are basically consistent with that of the global fitting method. The normal configuration of alizarin molecule 9,10-ketone molecule is in a trend of the rapid decrease in 110.5 femtoseconds, while the tautomeric configuration 1,10-ketone molecule is in a tendency of the fast increase in this time scale. When the delay time increases, it decays slowly for 1,10-ketone tautomeric configuration of the alizarin molecule.